This invention relate s generally to the making of extruded plastic bag making material equipped with separable fastener means, and is more particularly concerned with improvements over the disclosure in my recently issued U.S. Pat. No. 4,701,361 dated Oct. 20, 1987.
In my aforesaid patent, is disclosed a method of and an apparatus for producing plastic film with transverse closure strips and especially adapted for making bags. A plastic film tube is continuously extruded along a given longitudinal axis, and there is joined with a surface of the tube closure strip means having a longitudinal strip axis which extends across the tube axis in generally helical fashion. The tubular film is converted into ribbon sheet form with the closure strip means extending as individual closure strips across the ribbon sheet form at longitudinally spaced intervals. In the extrusion of the plastic film tube, according to that disclosure the tube diameter is maintained substantially the same as the extrusion orifice of the extruder. Such arrangement permits only a longitudinal axial orientation in the film.
However, for improvement in the water vapor transmission rate of high density polyethylene a biaxial orientation in the film structure is desirable. A general arrangement for attaining the biaxial orientation in the film tube is disclosed in U.S. Pat. Re. 29,208, but therein coextruded fastener strip means extends strictly longitudinally parallel to the axis of the tube through all phases of its manufacture and conversion into bag material.